Abstract. Wood is renewable stock that is used for shield, heating and defence since the times men emerged. Wood product dimensional alterations are a serious drawback in the wood practical applications. These alterations are caused by atmospheric moisture absorbance into wood and water interaction with hemicelluloses and cellulose amorphous part hydroxyl groups to entail wood swelling or shrinking in the case of wood drying that leads to wood products cracking and properties loss. It is assumed that the accessible to water hydroxyl group's hydrogen atom substitution with more voluminous and less polar organic radical arouse wood permanent swelling or hydroxyl group shielding. Modified wood has less water absorption and diminished water equilibrium content (EMC) that is considered as the main reason of biological resistance improvement. Wood furfurylation with furfuryl alcohol (FA) catalysed with maleic anhydride (MA) is one of the wood modification approaches. Wood dimensional stability and biological resistance to decay increase by modification with furfuryl alcohol FA is assumed as a result of FA polymers grafting to cell wall polymers. Sufficient amount of FA must be infused into wood cell walls, but FA diffusion into the wood cell wall might be hampered by formation of more voluminous π-complex between MA and FA that favour useless polymerisation in wood voids and increased FA and MA consumption. The objective of the given research was to attain maximal modification of the wood cell wall by saturation with FA and subsequent its polymerization by catalysis with formic acid vapour. Assessment of furfurylated and reference wood specimens durability in hot water -freezing -drying treatment was tested by the cyclic hydrothermal treatment (CHT) test. Wood furfurylation decreased water absorption by 80 % and swelling by 40 % during CHT in comparison with untreated wood.